Abstract:

Papermaking felts include a base material and a batt layer provided on one
or both sides of the base material. The batt layer includes a
water-absorbing resin, and the water-absorbing resin has a coefficient of
water absorption of from 1.05 and 10.

Claims:

1. A papermaking felt, comprising:a base material; anda batt layer
provided on one or both sides of the base material;wherein:the batt layer
comprises a water-absorbing resin; andthe water-absorbing resin has a
coefficient of water absorption of from 1.05 and 10.

7. The papermaking felt according to claim 1, wherein a dry resin weight
of the water-absorbing resin is from 0.5 to 30 wt. % relative to a total
weight of the felt without the water-absorbing resin.

8. The papermaking felt according to claim 1, wherein the water-absorbing
resin comprises at least one filler selected from the group consisting of
titanium oxide, kaolin, clay, and talc.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001]This application is a continuation of International Application No.
PCT/JP2010/001933, filed Mar. 18, 2010, the disclosure of which is
incorporated herein by reference in its entirety. This application claims
priority to Japanese Patent Application No. 2009-068458, filed Mar. 19,
2009, and Japanese Patent Application No. 2009-138461, filed Jun. 9,
2009, the disclosures of which are incorporated herein by reference in
their entireties.

BACKGROUND

[0002]The present invention relates to a papermaking felt (hereinafter
also called "felt") used for squeezing water from inside a wet paper web,
onto which it is stacked, by a pair of rotating rolls or by a roll and a
shoe of a papermaking machine. More particularly, the present invention
relates to a papermaking felt for improving the capability to squeeze
water from the wet paper web during the period including from the initial
warming-up period to the top speed operation of papermaking machines at
which constant production is possible.

[0003]Conventionally, papermaking machines in the papermaking process are
generally equipped with a wire part, a press part and a dryer part to
dewater wet paper webs. These parts are provided in the direction in
which the wet paper web is transferred in the order of: wire part, press
part and dryer part. The wet paper web is dewatered and, at the same
time, transferred while being passed from one papermaking equipment to
the next provided in the wire part, press part and dryer part,
respectively, to be finally dried in the dryer part.

[0004]Papermaking equipment for dewatering is provided corresponding to
each of these parts. The press device provided in the press part
comprises a plurality of press devices arranged in series in the
direction in which the wet paper web is transported.

[0005]Each press device comprises an endless felt or an open-ended felt
that has been made into an endless felt by connecting it in the
papermaking machine and, as a press, a pair of rolls (i.e., a roll press)
or a roll and a shoe (i.e., a shoe press), which are provided so as to
face each other and pinch therebetween one part of the felt,
respectively, from above and below; wherein pressure is applied on a wet
paper web, which is transported by a felt traveling at substantially a
same speed and in the same direction, together with the felt by one roll
and the other roll or between the roll and the shoe, whereby the moisture
in a wet paper web is squeezed out and is being continuously absorbed by
the felt.

[0006]Moreover, among these types of papermaking machines there are some
that have a roll press mechanism, provided in the press device of the
press part, for pressing while pinching, between one roll and the other
roll, one part of the felt(s) holding the wet paper web (therebetween),
while others have a shoe press mechanism, provided in the press device of
the press part, for pressing while pinching, between the roll and the
shoe, one part of the felt(s) holding the wet paper web (therebetween).

[0007]The felt is made from a base material and (a) batt layer(s); the
batt layer(s) is (are) provided both on the wet paper web carrying-side
and on the press roll-side of the base material or only on the wet paper
web carrying side. The batt layer is made by intertwiningly integrating
batt fibers with the base material by needle punching. The felt basically
has the functions of squeezing water from the wet paper web (water
squeezing capability), of increasing the smoothness of the wet paper web
and of transferring the wet paper web.

[0008]Above all, what is considered to be important in a felt is the
function of dewatering the wet paper web, the ability to maintain
compressibility and water permeability, resulting from a suitable free
space volume in the felt, for discharging water that has moved from the
wet paper web to the felt due to passing the pressure between the pair of
rolls or the roll and the shoe, to the outside of the felt system.

[0009]The suitable free space volume is the free space volume during
constant speed operation of a papermaking machine. From the viewpoint of
productivity, it is important that the operating speed stabilizes
rapidly; the time until this happens is called the initial warming-up
period. The initial warming-up period differs according to the operating
conditions of the papermaking machine; however, in general one to two
days, at most five days, are required. In particular, with the no-draw
straightthrough type of wet paper transfer method, of which the
Tandem-Nipco Flex papermaking machine is a representative example, it is
important to shorten the initial warming-up period and to increase
operating speed.

[0010]Various conventional felts have been developed from this point of
view. For example, after a felt has been prepared, a commonly known
technique is to apply pressure to make the felt thinner during the
following processes and to increase the density. There are also cases in
which the felt is brought into contact with a roll that has been heated
by a heating medium in order to increase the effect of the pressing. The
operating mechanism is to reduce the free space volume in the felt and to
facilitate the transfer of the pressing force received in the press part
to the wet paper web.

[0011]In Patent document 1 (JP-T-2005-524002), a compacting method is
described in which the felt surface is polished after it has been treated
with a polymer substance. A felt of this structure is compacted from the
beginning; therefore, it leads to the shortening of the initial
warming-up period of the papermaking machine.

[0012]Nevertheless, even though a papermaking felt using the polyurethane,
polycarbonate urethane, polyacrylate, acryl resin, epoxy resin, phenol
resin or mixed polymers thereof according to Patent document 1 can be
compacted due to the adhesive force and the coagulating force of the
polymers, stiffness is given to the felt as a whole. When the stiffness
becomes too great, the compression/recovery behavior under the press is
suppressed and sufficient wet paper web water squeezing performance
cannot be obtained; further, when the felt is placed in a papermaking
machine, together with the difficult operation of manually inserting the
felt into the narrow space between the rolls, there is also a problem
with regard to the easiness of loading the felt.

[0013]In Patent document 2 (JP-A-02-127585), a manufacturing method for
coating a foam resin onto a felt surface and for drying and curing the
same is described. In a felt of this structure, the felt surface, which
due to the foam resin has a porous contact region, removes the water from
the wet paper web.

[0014]Nevertheless, in the felt described in Patent document 2, the porous
part can receive the moisture that is squeezed from the wet paper web
when it is new; however, under the direct impact of the repeated pressure
from the press roll, the felt, including the porous part, is gradually
compacted. There is the problem that the water squeezing capability
deteriorates because, when the foam resin layer is compacted, the water
permeability decreases, and when it accumulates dirt from the wet paper
web, it becomes impossible to receive the moisture from the wet paper
web.

[0015]Patent document 3 (JP-A-2005-146443), which employs the same type of
foam resin, proposes a production method, wherein a layer (wall
structure) is provided by a foam gel inside the wet paper web contact
layer on the felt base material. In a felt of this structure, which has
good pressure dispersion, base fabric marking is prevented and the
surface smoothness of the wet paper web is improved.

[0016]Nevertheless, in the felt described in Patent document 3, even
though the gel foam layer is not in direct contact with the press roll,
there is the same problem as in Patent document 2.

[0017]With the felt described in Patent document 4 (JP-A-56-53297), it can
be expected that the initial warming-up period is shortened due to the
hydrophilic properties of the sodium acrylate-acrylamide copolymer
fibers.

[0018]Nevertheless, with the felt described in Patent document 4, there is
the problem that the ability to maintain the water squeezing capability
deteriorates, because the durability of the sodium acrylate-acrylamide
copolymer fibers is low. There is further the problem that the fibers of
low durability are shed from the felt and get attached to the paper,
which is a hindrance during printing.

SUMMARY

[0019]With these types of conventional felts, the initial warming-up
period is short; however, there is the problem that, since the free space
inside a felt which has been made thin from the beginning is reduced, the
felt is crushed by the repeated pressure received during use and rapidly
arrives at the limit of the thickness at which it can be used; thus the
time during which the wet paper web can be sufficiently squeezed is
short.

[0020]Moreover, when the press force is increased during the production
process in order to reduce the free space even further, the fibers
constituting the felt hit against each other and it has to be feared that
fibers are lost because pressure marks remain at the points the fibers
intermingle and strength deteriorates.

[0021]An object of the present invention is to solve the reciprocal
problems of shortening the initial warming-up period and of ensuring the
constant operation period.

[0022]In particular, it is the object of the present invention to provide
a papermaking felt, wherein the basic functions are well balanced, which
does not have any wet paper web transfer deficiencies due to meandering,
or the like, wherein, free space of a felt, in which the effect of the
press pressure and the hydraulic pressure is scarcely conveyed to the wet
paper web from which water is squeezed, is set to the suitable amount for
the initial warming-up from the start so that the initial warming-up
period is shortened, and wherein water squeezing does not deteriorate due
to premature decline of water permeability and due to the inability to
maintain compressibility by excessive compaction and accumulation of
dirt.

[0023]The present invention was made by discovering that, by including a
water-absorbing resin in a papermaking felt, it is possible, both, to
appropriately ensure a free space volume in a felt after water is
absorbed and to maintain compressibility; thus the invention was
completed. In order to solve the above-mentioned problems, the present
invention is characterized in that a water-absorbing resin is included in
a batt layer of a papermaking felt made from a base material and at least
a wet paper web stacking side batt layer. Specifically, the present
invention is based on the technology described hereinafter.

[0024](1) A papermaking felt wherein a batt layer is provided on one side,
or on both sides, of a base material, and wherein a water-absorbing resin
with a coefficient of water absorption between 1.05 and 10 is included in
the batt layer of said felt.

[0025](2) A papermaking felt according to (1); wherein said
water-absorbing resin comprises a urethane structure obtained by reacting
(a) polyisocyanate compound(s) selected from the compounds of component
[a] and (a) polyol compound(s) selected from the compounds of component
[b]:

[0032](7) A papermaking felt according to any one of (1) to (6); wherein
the dry resin weight of the water-absorbing resin is 0.5 to 30 wt. % of
the felt weight before including the resin.

[0033](8) A papermaking felt according to any one of (1) to (7); wherein
the water-absorbing resin comprises one or more filler(s) such as
titanium oxide, kaolin, clay, talc, or the like.

[0034]In the papermaking felt according to the present invention, due to
the water-absorbing action of the water-absorbing resin, the free space
volume is reduced in a felt in which the effect of the press pressure and
the hydraulic pressure is scarcely conveyed to the wet paper web, and the
initial warming-up period is shortened. Moreover, since compressibility
is maintained due to the flexibility and durability of the resin that is
swollen by water, the water draining capability can be maintained
together with an improvement of the ability to maintain elasticity, as
will be shown in the Examples.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]A more complete appreciation of the invention and many of the
attendant advantages thereof will be readily obtained as the same becomes
better understood by reference to the following detailed description when
considered in connection with the accompanying drawings, wherein:

[0036]FIG. 1 is a view showing a felt according to the present invention
in which the water-absorbing resin stays in the front-side (wet paper web
contact side) batt layer.

[0037]FIG. 2 is a view showing a felt according to the present invention
in which the water-absorbing resin reaches from the front-side batt layer
to the rear-side batt layer.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0038]The drawings show one example of a papermaking felt according to the
present invention. The present invention is, however, not limited to the
specific example shown in the drawings. The example of a papermaking felt
shown in the drawings comprises a base material 1, a batt layer 2, and a
rear batt layer 3 disposed on the press roll-side of the base material;
in FIG. 1, the water-absorbing resin 4 stays in the wet paper web
carrying-side batt layer 2; in FIG. 2, the water-absorbing resin 4
reaches the press roll-side batt layer 3. The wet paper web-side batt
layer 2 includes batt fiber and water-absorbing resin 4 which fill a part
of the space formed by the batt fiber. The machine direction yarn (MD
yarn) 1a and the cross machine direction yarn (CMD yarn) 1b are also
shown in FIGS. 1 and 2.

[0039]In general, a papermaking felt is made by batt layers sandwiching a
base material. The base material is generally a fabric woven by a weaving
machine, or the like, from a machine direction yarn and a cross machine
direction yarn. Examples of materials used for the machine direction and
cross machine direction yarns of the base material and for the batt
include polyesters (polyethylene terephthalate, polybutylene
terephthalate, or the like), polyamides (nylon 6, nylon 66, nylon 610,
nylon 612, or the like), polyphenylene sulfide, polyvinylidene fluoride,
polypropylene, aramid, polyetheresterketone, polytetrafluoroethylene,
polyethylene, polyvinyl chloride, cotton, wool, metal, or the like.

[0040]<Types of Water-Absorbing Resin>

[0041]As water-absorbing resin, one or more water-absorbing resin(s) of
natural polymers or synthetic polymers with a coefficient of water
absorption between 1.05 and 10 can be used.

[0047]Examples of urethane water-absorbing resins include denaturated
polyols, wherein hydrophilic polyol is reacted with polyisocyanate, in
which the hydrophilic polyol is obtained by addition polymerization on
polyhydric alcohol of ethylene oxide on its own or with ethylene oxide
and propylene oxide, and blended polyols, wherein a water-absorbing resin
of starch, PVA, or the like, is blended in polyol and reacted with
isocyanate, or the like. Among these, a water-absorbing resin, wherein
hydrophilic polyol is reacted with polyisocyanate, in which the
hydrophilic polyol is obtained by addition polymerization on polyhydric
alcohol of ethylene oxide (EO) and propylene oxide (PO), is preferred.

[0049]Examples of the above-mentioned polyols include aromatic hydrophilic
polyols obtained by addition polymerization on aromatic polyhydric
alcohol of EO or PO. Preferred aromatic polyhydric alcohols are
4,4'-dihydroxy phenyl sulfone, resorcine, 1,4-bis hydroxyethoxy benzene.
Among these, polyether polyols obtained by reacting polyether polyols in
which the amount of the oxyethylene groups is between 40 and 100% of the
weight in the polyoxy alkylene, and polyether polyol with a molecular
weight of 1000 or less and in which the amount of oxyethylene groups is
between 0 and 30% of the weight in the polyoxy alkylene are preferred.

[0050]<The Form of the Water-Absorbing Resins>

[0051]The shape of the water-absorbing resins included in the batt layer
of the papermaking felt is not particularly limited, it may be in the
form of particles or it may be in the form of a dispersed film. However,
a water-absorbing resin that, after water absorption, forms a continuous
film layer like a sheet hinders water permeability is not preferred.

[0052]<Coefficient of Water Absorption>

[0053]The coefficient of water absorption is measured by the following
method.

[0054]1. The weight of a specimen (water-absorbing resin), measured up to
an accuracy of 0.01 g after drying for one hour at 105 degrees Celsius,
is defined as M1.

[0055]2. Suitable amounts of the specimen (for example 100 g) are filled
into bags of nonwoven fabric, one nonwoven fabric bag at a time is
completely immersed in an immersion liquid obtained from a sufficient
amount of pure water of 20 degrees Celsius +-2 degrees Celsius.

[0056]3. The nonwoven fabric bags with the specimen are taken out of the
immersion liquid at intervals of one hour and are introduced into a
rotary dewatering machine (a Sheet Former manufactured by Kumagai Riki
Kogyo Co., Ltd.).

[0057]4. The rotational speed of the Sheet Former is set so as to obtain a
prescribed speed of 1500 m/min., and dewatering is performed for a
prescribed time (5 minutes) after the speed reaches the set value (after
12 seconds).

[0058]5. After dewatering has continued for 5 minutes, brakes are applied
to stop the centrifugal dewatering. The total weight of the dewatered
nonwoven fabric bag and the specimen are measured up to an accuracy of
0.01 g.

[0059]6. Thereafter, steps 3. to 5. are repeated, and the total weight of
the specimen and the nonwoven fabric bag at the time there is no more
weight increase is defined as M2.

[0060]7. The nonwoven fabric bag is immersed in the pure water on its own,
and the weight of the nonwoven fabric bag measured according to steps 3.
to 5. above is defined as S1; the value of the coefficient of water
absorption is obtained according to the formula: coefficient of water
absorption=(M2-S1)/M1.

[0061]The coefficient of water absorption is preferably between 1.05 and
10.

[0062]The location in which these water-absorbing resins are included in
the papermaking felt is not particularly limited; however, they are
preferably included in a region from the wet paper web carrying-side batt
layer to the base material. Specifically, the water-absorbing resins may
be included only in the wet paper web carrying-side batt layer 2, in the
region from the wet paper web carrying-side batt layer 2 to the press
roll-side batt layer 3, in the region from the wet paper web
carrying-side batt layer 2 to the base material 1, or in the region from
the press roll-side batt layer 3 to the base material 1.

[0063]The means for including the water-absorbing resin in the felt
include such techniques as coating-impregnating, spray coating, blade
coating, or the like, of the felt with an aqueous dispersion liquid in
which water-absorbing resin particles have been dispersed in an aqueous
solution.

[0064]A cross-linking agent may be used as needed for causing the
water-absorbing resin to hold firmly to the felt; the cross-linking agent
is coated in a dispersed form in the above-mentioned aqueous dispersion
liquid, and thereafter cross-linking reaction is performed by heating or
by electron beam radiation. Examples of cross-linking agents include, for
example, polyethylene glycol mono(meta) acrylate, N-methylol (meta)
acrylamide, glycidyl (meta) acrylate, polyethylene glycol di(meta)
acrylate, N,N-methylene bis(meta) acrylamide, or the like, and diglycidyl
ether or polyglycidyl ether of ethylene glycol diglycidyl ether,
polyethylene glycol diglycidyl ether, fatty polyhydric alcohol, or the
like, and mixtures thereof. Moreover, one or more types of cross-linking
agent(s) may be used.

[0065]The free space volume, which can be obtained in a papermaking felt
apart from the fibers, is preferably maintained at a fixed volume from
the initial warming-up period to the transition of the operating speed to
the top speed region, at which constant production is possible, until the
final period of operation is reached. Therefore, the losing speed of the
water absorbed resin from the felt may be controlled in the view of the
operating conditions and the amount of water removed from the wet paper
web.

[0066]The used amount of the cross-linking agent is determined by the
molar equivalent of the reactive groups (isocyanate groups in the case of
urethane-based water-absorbing agents) of the water-absorbing agent and
the molar equivalent of the reactive groups (active hydrogen groups) of
the cross-linking agent. The durability after the cross-linking is
controlled by adjusting a suitable equivalent ratio (--NCO/--H).
Specifically, an equivalent ratio of 0.7 to 1.5 is preferred.

[0067]According to the present invention, a papermaking press felt can be
obtained which can improve the water squeezing capability from a wet
paper web during the entire period of use including the initial
warming-up period and until the top speed of a papermaking machine is
reached at which constant production is possible, which can be installed
in a papermaking machine with the same load as used for conventional
felts, and which is of practical utility in the papermaking industry.

[0068]Other features of the invention will become apparent in the course
of the following descriptions of exemplary embodiments which are given
for illustration of the invention and are not intended to be limiting
thereof.

EXAMPLES

[0069]Hereinafter, the present invention will be described by the Examples
and the Comparative Examples. The present invention is, however, not
limited to these Examples.

[0070]Examples 1 to 6, Comparative Examples 1 and 2

[0071]The papermaking felts used in the Examples and Comparative Examples
had the following basic configuration:

[0077]Furthermore, the weight of the filler is used in the ratio of 8 wt.
parts per 100 wt. parts of water-absorbing resin. The coefficient of
water absorption of the water-absorbing resin used for the papermaking
felts obtained and the amount of water-absorbing resin attached to the
felt in the dried state after curing are shown in Table 1. The percentage
amount of dried water-absorbing resin attached to the felt represents the
ratio of the weight (dry weight) of water-absorbing resin attached to the
felt per 100 wt. parts of felt material before the water-absorbing resin
is attached.

[0078]The papermaking felts that were obtained in the Examples 1 to 6 and
the Comparative Examples 1 and 2 were tested under the traveling test
conditions described hereinafter for 100 hours at a traveling speed of
1,000 m/min. and under a roll pressure of 100 kN/m; the water squeezing
capability, the ability to maintain elasticity and the ability to
maintain water permeability were evaluated.

[0084]The lower the wet paper web moisture content after pressing, the
better is the water squeezing capability of the papermaking felt; in the
papermaking industry, even if the difference of the wet paper web
moisture content after pressing is only 1%, there is a significant impact
on the amount of thermal energy required in the paper drying process
after pressing.

[0085]Compression test; high speed press tester

[0086]Felt thickness before pressing; T0

[0087]Felt thickness during pressing; T1(100 kN/m)

[0088]Felt thickness after pressing; T2

[0089]Compression ratio (%)=(T0-T1/T0×100

[0090]Thickness maintaining ratio (%)=(T2/T0)×100

[0091]Water percolation test; water percolation tester

[0092]Water percolation value; 20 MPa pressure; a metal plate having been
disposed on one side of a 120 mm f felt sample, the time required for 5
liters of water to pass at a hydraulic pressure of 3 MPa from the side
without metal plate.

[0096]Table 2 shows that the lower the wet paper web moisture content
after pressing, the better is the water squeezing capability, and that
the higher the compression ratio of the pressing and the before/after
pressing thickness maintaining ratio, the better are the elasticity
maintaining properties.

[0097]In the papermaking felts of Examples 1 to 6, it can be seen that the
water squeezing capability and the elasticity maintaining ratio is
improved due to the swelling of the water-absorbing resin in the felts.

[0098]Moreover, the papermaking felts of Examples 1 to 6 exhibit high
values of water percolation maintaining ratio; the reason for this is
that, due to the water-absorbing resin, the excessive free space at the
time the felt is new is closed, and due to the gradual loss of resins
occurring together with use, the felts possess a suitable water
permeability from the initial warming-up to the final period of
operation.

[0099]Where a numerical limit or range is stated herein, the endpoints are
included. Also, all values and subranges within a numerical limit or
range are specifically included as if explicitly written out.

[0100]Obviously, numerous modifications and variations of the present
invention are possible in light of the above teachings. It is therefore
to be understood that, within the scope of the appended claims, the
invention may be practiced otherwise than as specifically described
herein.

[0101]All patents and other references mentioned above are incorporated in
full herein by this reference, the same as if set forth at length.